Associations between polymorphisms and haplotypes of the bovine CD4 and IFN-γ genes with mastitis susceptibility in Italian simmental cattle.

This study aimed to investigate the potential association between the breeding values for somatic cell scores in milk (SCS) and polymorphisms in genes that encode for cytokines (CXCL8, TGF-β1 and IFN-γ) and CD4. These genes were selected because of their critical roles in immune regulation and their known involvement in mastitis-related inflammatory processes. To gain a comprehensive breeding perspective, the association study was conducted simultaneously with breeding values for productive traits in 558 Italian Simmental cows, a widespread dual-purpose dairy and beef bovine breed that is adaptable to harsh farming and breeding conditions.The association analysis showed that only three of the nine chosen markers, one in IFN-γ and two in CD4, significantly associated with somatic cell breeding values, without effects on the other dairy traits. Only one of the two CD4 SNPs has been considered, being in linkage disequilibrium. The two remaining SNPs were grouped into three haplotypes (A-G, 88%; A-A, 5%; and T-G, 7%, respectively), and Haplotype-3 significantly affected the breeding values for SCS. The combination of Haplotype-1 with Haplotype-2 resulted in a significant decrease, while with Haplotype-3 led to a considerable improvement in SCS breeding values. It was noted that the functional haplotypic combinations examined did not significantly affect the production breeding values. This research could provide interesting polymorphisms for genomic evaluation of Italian Simmental dairy cows, increasing the accuracy of breeding values, assisting breeders in selecting animals with enhanced immune responses, minimising the economic impact of mastitis, and improving overall herd health and productivity.